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29 juin

Rainer Friedrich Deconstructing and reconstructing neuronal circuits for olfaction

Invité par German Sumbre

11h à 12h30

Le séminaire de Rainer FRIEDRICH (Friedrich Miescher Institute for Biomedical Research, Basel, Switzerland) aura lieu dans la salle Favard, IBENS 46 rue d’Ulm 75005 Paris

We use the olfactory system of zebrafish as a model to explore how higher brain functions emerge from elementary neuronal computations. The small size of the zebrafish brain allows for measurements of neuronal activity patterns across large fractions of neurons by multiphoton calcium imaging, even in adults. Moreover, the small brain size facilitates optogenetic manipulations of neuronal activity patterns and the exhaustive reconstruction of neuronal circuits by serial block face scanning electron microscopy (SBEM). The olfactory bulb, the first olfactory processing center in the vertebrate brain, transforms odor-evoked activity patterns across its input channels, the olfactory glomeruli, into spatio-temporal activity patterns across its output neurons, the mitral cells. In adult zebrafish, we uncovered computations associated with this transformation that are likely to define the main functions of the olfactory bulb. One computation is an “equalization” that stabilizes odor representations against variations in stimulus intensity and is performed by a distinct microcircuit involving GABAergic inhibition and gap junction coupling. Another computation is a “decorrelation” that reduces the overlap between representations of chemically similar odors and thereby facilitates the discrimination of odor representations in higher brain areas. Recently, we reconstructed the complete set of neurons in the larval olfactory bulb using SBEM. Topological analyses of circuit structure revealed a specific organization of long-range connectivity that is governed by the identity of olfactory glomeruli. These results provide insights into the structure and function of neuronal circuits that are likely to be of fundamental importance and illustrate the power of zebrafish as a model in systems neuroscience.